A semiconductor device using a direct bond substrate, for example, a substrate having a direct silicon bond (DSB) has a structure in which hybrid-orientation-technology can be used and which does not have a silicon-on-insulator (SOI) structure. The DSB substrate does not have buried oxide (BOX) unlike the SOI substrate. Therefore, ideally, nothing other than silicon is provided on an interface on which silicon layers having different plane orientations (crystal orientations) are bonded together.
Direct Silicon Bonded (DSB) is a bulk CMOS hybrid orientation technology that can exploit the higher electron and hole mobility expected from Silicon surfaces. Regarding hybrid orientation fabrication and technology, a twist-angle-optimized direct silicon bonded substrate can be formed. The bonding process can include the bonding of two semiconductor layers that have different surface orientations at an optimal azimuthal twist angle. The azimuthal twist angle can be the angle formed between notches made in a semiconductor wafer corresponding to a crystalline direction. The azimuthal twist angle is the angle between the notches or respective crystalline directions when the wafers are direct Silicon bonded to one another.
With a selected twist angle of 45 degrees between the crystalline layers, an improvement in the morphology of the defective boundary regions can be achieved. DSB in combination with the twist angle of 45 degrees can enable a PFET to have higher mobility compared to conventional substrates without degrading electron mobility for an NFET. Additionally, two layers that are Direct Silicon Bonded together with a 45 degree twist angle an show higher hole mobility in comparison to a DSB substrate with zero degree twist angle. Yet, the bonded interface between the two layers that are DSB together can cause high junction leakage current.